There has been known that, in chronic pain patients suffering from tension-type headache, temporomandibular disorder, and the like, a sensory nerve is sensitized in peripheral and central nervous systems, with the result that abnormalities such as hypersensitivity, increased responsiveness, and enlargement of receptive fields occur in some cases. When a peripheral nerve or a central nerve is sensitized with pain, pain is intensified, and a range of pain is enlarged. Consequently, a patient feels pain even in a site in which the patient does not usually feel pain. When central sensitization is caused by chronic headache, temporomandibular disorder, and the like, in most cases, symptoms are not alleviated even if standard therapies for original headache and temporomandibular disorder are conducted, and treatments using an antidepressant and the like acting on the central nervous system are required. At least several percentages of the patients with headache, temporomandibular disorder, and the like are considered to have such central sensitization, and treatments to be conducted totally vary depending on whether the patients have mere headache, temporomandibular disorder, and the like, or have central sensitization. Therefore, it is very important to diagnose the presence or absence of the central sensitization.
However, the central sensitization can be diagnosed only by, for example, a detailed medical interview performed by experienced physicians or confirmation of a response to mechanical stimulation, and hence the diagnosis thereof is not easy.
Consequently, in spite of the fact that a patient has central sensitization, the patient is diagnosed to have mere temporomandibular disorder or the like. Then, it is predicted that such a situation frequently occurs that, although provided with a therapy for temporomandibular disorder, the patient is not improved in the symptom and goes to another hospital for seeking a second opinion. This is considered to serve as a factor for so-called “doctor shopping” in which a patient visits various hospitals.
According to the US actual situation survey in 1998 to 1999, the ratio of patients suffering from chronic pain at a medium level or more is determined to be 9% of the adult population. Then, the social economic loss caused by the waste of medical fees caused by ineffective treatments and doctor shopping and difficulty in working due to pain and the like is estimated to be about 9 trillion yen per year.
Under such circumstances, there is a demand for establishing a quantitative sensory test (QST) as an objective examination method for central sensitization.
On the other hand, hitherto, patients with temporomandibular disorder and the like have been evaluated for temporal summation (TS) of pain sensation caused by continuous thermal stimulation. The TS is a phenomenon in which, in spite of the fact that thermal stimulation increasing or decreasing continuously is performed with a temperature width and stimulus sensation being constant, pain intensity felt by a subject increases gradually as the number of stimulation increases to 5 times, 10 times, and 15 times. Then, Non Patent Literature 1 discloses that, when such thermal stimulation is applied, aftersensations are caused in a test site even after the end of the stimulation. However, Non Patent Literature 1 merely evaluates the difference in aftersensations between a patient with temporomandibular disorder and a healthy subject and does not at all disclose a method of discriminating a temporomandibular disorder patient and a chronic temporomandibular disorder patient with central sensitization.